Techniques to determine transmitter power

ABSTRACT

Techniques are described that can be used to determine a transmitter power level of a mobile station based on spectrum efficiency gain and loss. Spectrum efficiency gain is measured for a home sector base station. Spectrum efficiency loss is measured for base stations other than the home sector base station. In one example, a base station transmits information such as noise plus interference level to a mobile station and the mobile station determines the transmitter power level. In another example, the mobile station transmits information such as preamble signal strength and preamble total signal strength to the home sector base station and the home sector base station determines the transmitter power level and instructs the mobile station to apply the determined transmitter power level.

FIELD

The subject matter disclosed herein relates generally to techniques todetermine transmitter power of a wireless signal.

RELATED ART

In wireless networks, determination of wireless signal strength is animportant decision. Increasing transmission power of one mobile stationenjoys the increase of its link performance but increases interferencesto other mobile stations of neighboring base stations because they usethe same channel. This results in decreased link performance of theother mobile stations. Therefore, in deciding transmission power, it isimportant to balance the performance of a particular link withinterference to the other base stations.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the drawings and in which likereference numerals refer to similar elements.

FIG. 1 depicts a process that can be used to determine a transmitterpower for a mobile station, in accordance with an embodiment.

FIG. 2 depicts in block diagram format a system that determinestransmitter power using Open Loop Power Control (OLPC), in accordancewith an embodiment.

FIG. 3 depicts a block diagram of a system that determines thetransmitter power of a mobile station using Closed Loop Power Control(CLPC), in accordance with an embodiment.

FIG. 4 depicts scenarios in which CLPC or OLPC may be used to determinetransmitter power, in accordance with an embodiment.

FIG. 5 depicts a Cumulative Distribution Function of throughput for asimulation.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrase “in one embodiment” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in one or moreembodiments.

Embodiments of the invention may be used in a variety of applications.Some embodiments of the invention may be used in conjunction withvarious devices and systems, for example, a transmitter, a receiver, atransceiver, a transmitter-receiver, a wireless communication station, awireless communication device, a wireless Access Point (AP), a modem, awireless modem, a Personal Computer (PC), a desktop computer, a mobilecomputer, a laptop computer, a notebook computer, a tablet computer, aserver computer, a handheld computer, a handheld device, a PersonalDigital Assistant (PDA) device, a handheld PDA device, a network, awireless network, a Local Area Network (LAN), a Wireless LAN (WLAN), aMetropolitan Area Network (MAN), a Wireless MAN (WMAN), a Wide AreaNetwork (WAN), a Wireless WAN (WWAN), devices and/or networks operatingin accordance with existing IEEE 802.11, 802.11a, 802.11b, 802.11e,802.11g, 802.11h, 802.11i, 802.11n, 802.16, 802.16d, 802.16e, 802.16m,or 3GPP standards and/or future versions and/or derivatives and/or LongTerm Evolution (LTE) of the above standards, a Personal Area Network(PAN), a Wireless PAN (WPAN), units and/or devices which are part of theabove WLAN and/or PAN and/or WPAN networks, one way and/or two-way radiocommunication systems, cellular radio-telephone communication systems, acellular telephone, a wireless telephone, a Personal CommunicationSystems (PCS) device, a PDA device which incorporates a wirelesscommunication device, a Multiple Input Multiple Output (MIMO)transceiver or device, a Single Input Multiple Output (SIMO) transceiveror device, a Multiple Input Single Output (MISO) transceiver or device,a Multi Receiver Chain (MRC) transceiver or device, a transceiver ordevice having “smart antenna” technology or multiple antenna technology,or the like. Some embodiments of the invention may be used inconjunction with one or more types of wireless communication signalsand/or systems, for example, Radio Frequency (RF), Infra Red (IR),Frequency-Division Multiplexing (FDM), Orthogonal FDM (OFDM), OrthogonalFrequency Division Multiple Access (OFDMA), Time-Division Multiplexing(TDM), Time-Division Multiple Access (TDMA), Extended TDMA (E-TDMA),General Packet Radio Service (GPRS), Extended GPRS, Code-DivisionMultiple Access (CDMA), Wideband CDMA (WCDMA), CDMA 2000, Multi-CarrierModulation (MDM), Discrete Multi-Tone (DMT), Bluetooth (RTM), ZigBee(TM), or the like. Embodiments of the invention may be used in variousother apparatuses, devices, systems and/or networks. IEEE 802.11x mayrefer to any existing IEEE 802.11 specification, including but notlimited to 802.11a, 802.11b, 802.11e, 802.11g, 802.11h, 802.11i,802.11n.

Some embodiments determine transmitter power of a mobile station basedon spectrum efficiency. Spectrum efficiency gain for a home sector basestation is measured for a transmitter power level. Spectrum efficiencyloss for other base stations is measured for the same transmitter powerlevel. If the spectrum efficiency gain is less than or equal to spectrumefficiency loss, then the transmitter power level is used by a mobilestation. If the spectrum efficiency gain exceeds spectrum efficiencyloss, then the transmitter power level is incremented to another leveland spectrum efficiency gain and loss are determined for the otherlevel. In some embodiments, the mobile station determines its owntransmitter power level, whereas in some embodiments, a base stationdetermines the transmitter power level of the mobile station. Techniquesdescribed herein can be applied to OFDMA-based wireless broadbandtechnologies and related products, such as but not limited to IEEE802.16e, IEEE 802.16m, 3GPP LTE, and 3GPP UMB c, to increase systemuplink throughput (i.e., transmission rates from mobile station to basestation) significantly with acceptable interference to other basestations.

FIG. 1 depicts a process 100 that can be used to determine a transmitterpower P_(X) for a mobile station, in accordance with an embodiment.Block 102 may include establishing a trial transmitter power level. Thetransmitter power level, P_(Trial), can be initialized to zero andincreased by step ΔP for each iteration of process 100. P_(Trial)represents the current trial transmitter power level.

Block 104 may include determining spectrum efficiency (SE) gain andloss, respective SE_(gain) and SE_(loss), for the trial transmitterpower level. The key input parameters to determine SE_(gain) andSE_(loss) are path loss (PL) and noise plus interference level (NI).Techniques for determining path loss and noise plus interference levelare well known and described, for example, in sections 8.3.7.4.2,8.4.10.3.2, 8.4.11.3, 8.4.5.3.19, and 8.3.9.3 of IEEE 802.16 Rev2/D7(October 2008). Path loss PL₀ represents the path loss from a mobilestation to its home sector base station whereas path loss PL₁, PL₂, . .. , PL_(N) represent the path loss from the mobile station to the top Nbase stations that are interfered most significantly by this mobilestation on uplink. The mobile station receives a strongest signal fromthe home sector base station.

Noise plus Interference level (NI) is expressed as the sum power levelof noise and interferences. NI₀ represents a noise plus interferencelevel of a home sector station whereas NI₁, NI₂, . . . , NI_(N)represent noise plus interference level of other base stations. NI₁,NI₂, . . . , NI_(N) may be exchanged among base stations by a networkconnection or may be approximated. NI can also be transformed from/toInterference Over Thermal (IoT) using the following relationship:

NI=IoT×P _(Noise) +P _(Noise)

where, P_(Noise) is the thermal noise power level. Thermal noise powerlevel can be calculated from the following formula: P_(dbm)=−174+10log(f), where f is the bandwidth of the communication system.

In an embodiment, spectrum efficiency gain at the home sector basestation for a mobile station can be determined using the followingformula:

${SE}_{gain} = {\log ( \frac{1 + {SINR}_{New}}{1 + {SINR}_{Orig}} )}$

where, SINR is Signal to Interference plus Noise Ratio,

-   -   SINR_(New) is the SINR for power level P_(Trial), and    -   SINR_(Orig) is the SINR for the trial transmitter power level

immediately before its increase by ΔP.

More specifically, for the home sector base station, the followingrepresent the original and new SINR:

${SINR}_{Orig} = \frac{P_{0}/{PL}_{0}}{{NI}_{0}}$${SINR}_{New} = \frac{( {P_{0} + {\Delta \; P}} )/{PL}_{0}}{{NI}_{0}}$

After increasing the power of this mobile station to the trialtransmitter power level, the spectrum efficiency gain can be representedas:

${SE}_{gain} = {\log ( {1 + \frac{\frac{\Delta \; P}{{PL}_{0}}}{{NI}_{0} + \frac{P_{0}}{{PL}_{0}}}} )}$

Spectrum efficiency loss to the base stations other than home sectorbase stations due to the power increase of the mobile station can beexpressed as:

${{SE}_{loss}(i)} = {{\log ( {1 + \frac{\Delta \; I_{i}}{{NI}_{i}}} )} - {\log ( {1 + \frac{\Delta \; I_{i}}{S_{i} + {NI}_{i}}} )}}$${where},{{\Delta \; I_{i}} = {\frac{\Delta \; P}{{PL}_{i}}\mspace{14mu} {and}}}$

S_(i)=P_(Noise)×SNR_(i) and represents the useful signal power at thei^(th) neighbor base station.

In an embodiment, spectrum efficiency loss can be represented as the sumof all spectrum efficiency losses at neighboring base stations otherthan the home sector base station using the following formula:

${SE}_{loss} = {\sum\limits_{i = 1}^{N}{{SE}_{loss}(i)}}$

Block 106 may include determining whether the relationship betweenspectrum efficiency gain and spectrum efficiency loss are acceptable forthe trial transmitter power, P_(Trial). In one embodiment, ifSE_(gain)>SE_(loss), then block 102 follows block 106 and process 100repeats. In a next iteration, the trial transmitter power, P_(Trial), isincreased by ΔP. However, if SE_(gain)<=SE_(loss), then P_(Trial) fromblock 102 is the decided transmitter power for the current selectedmobile station. Increasing a mobile station's power level will increaseits own SE gain, at the cost of SE loss in neighboring base stations.The condition SE_(gain)<=SE_(loss) indicates that the predicted SElosses in all neighboring base stations equals or outweighs the SE gainin the home sector. So if the condition is satisfied, increasing powerlevel further is not beneficial in terms of net SE change in allsectors.

The process of FIG. 1 can be used to determine transmitter power in OpenLoop Power Control (OLPC) and Closed Loop Power Control (CLPC)configurations. FIG. 2 depicts in simplified high level block diagramformat a system 200 that determines transmitter power using Open LoopPower Control (OLPC), in accordance with an embodiment. The NIinformation or IoT are exchanged between base station 210 andneighboring base stations (not depicted) by using a network (e.g.,backhaul network). Base station 210 broadcasts the collected NIinformation, i.e., its own and neighbor base stations' NI to mobilestation 220 and other local mobile stations (not depicted). If there isno information exchange among base stations, base station 210 maybroadcast to mobile station 220 its own noise plus Interference level asan approximation of noise plus interference levels for all basestations.

Mobile station 220 determines the estimated path loss PL₀, PL₁, PL₂, . .. , PL_(N) based on a preamble signal from base station 210. Preamblesignal is defined in sections 8.4.4.2 and 8.4.6.1.1 of IEEE 802.16Rev2/D7 (October 2008). For example, suitable techniques to determinepath loss estimation from the preamble signal strength from base station210 and neighboring base stations are described at page 693, lines 57-59and page 1113, lines 11-14 in IEEE 802.16 Rev2/D7 (October 2008). In anembodiment, mobile station 220 executes process 100 of FIG. 1 todetermine its transmitter power based on the estimated PL₀, PL₁, PL₂, .. . , PL_(N) and the noise plus interference levels provided by basestation 210.

FIG. 3 depicts a simplified high level block diagram of a system thatdetermines the transmitter power of a mobile station using CLPC, inaccordance with an embodiment. In this embodiment, base station 310 doesnot broadcast noise plus interference level (or Interference OverThermal) information to mobile station 320. Instead, mobile station 320reports information to base station 310 and base station 310 uses theinformation to determine path loss information results PL₀, PL₁, PL₂, .. . , PL_(N). In an embodiment, the information includes path lossestimation results using MAC level signaling based on a preamble signalstrength from base station 310 and neighboring base stations. In anotherembodiment, the information includes both preamble signal strength (forexample, Carrier to Interference-plus-Noise Ratio level) and preambletotal signal strength (signal strength including interference). Forexample, suitable techniques to determine path loss estimation from thepreamble signal strength from base station 310 and neighboring basestations or both preamble signal strength and preamble total signalstrength are described at page 693, lines 57-59 and page 1113, lines11-14 in IEEE 802.16 Rev2/D7 (October 2008). Base station 310 calculatespath loss based at least on reported information from mobile station320.

Base station 310 determines transmitter power using the process 100 ofFIG. 1 based on the path loss information and noise plus interferencelevel information. Noise plus interference level information may bedetermined in a manner described with regard to FIG. 2. Base station 310transmits the decided transmitter power to mobile station 320 so thatmobile station 320 can transmit signals using the decided transmitterpower.

FIG. 4 depicts scenarios in which CLPC or OLPC may be used to determinetransmitter power, in accordance with an embodiment. OLPC can be thedefault scheme to adjust uplink transmit power from a mobile station.OLPC may provide the slow power control for slow fading but has anadvantage of less signal overhead than that of CLPC. Signal overheadrefers to radio resources used to feedback the path loss and unicast thedecided power level. When data packets are transmitted, CLPC can beused. CLPC can piggyback information used to determine transmitter poweron the data traffic for the fast control. For example, only a few bitscombined with resource allocation information element (IE) (e.g.,downlink map or uplink map information element) can be used to transmitpower control information used to determine transmitter power. Downlinkmap and uplink map are defined, for example, at page 15, lines 24-26;page 83, section 6.3.2.3.2 in IEEE 802.16 Rev2/D7 (October 2008). Forgeneral status, CLPC may provide fast power control but incur signaloverhead for unicast of decided transmitter power to each mobilestation.

FIG. 5 depicts results of throughput for Cumulative DistributionFunction of a simulation for 2500 frames SLS result in which 250 framesare transmitted each trial over 10 trials. The sector spectrumefficiency is 0.9377 whereas 5% user throughput is 11.7 kbps (0.0063).Basic simulation parameters are listed as follows:

BW 10 Mhz Frequency reuse 1 Cell deployment 3 sectors/cell and 19 cellwrap-around The number of users 10/sector The number of strong 8interference Channel model e-ITU Ped B 3 km/h Permutation mode Wimax ULPUSC Site-to-Site distance 500 m

For the simulation, some approximation assumptions for input parameterswere performed. First, because accurate short term SNR_(i) is difficultto estimate, the long term average is used as an approximation:SNR_(i)=SNR(i)_(average). Accordingly, SE_(loss) is represented as:

${{SE}_{loss}(i)} \approx {{\log ( {1 + \frac{\Delta \; I_{i}}{{NI}_{i}}} )} - {\log ( {1 + \frac{\Delta \; I_{i}}{{NI}_{i} + {P_{Noise} \times {{SNR}(i)}_{average}}}} )}}$

In the case of OLPC, the path loss estimation will be the long termaverage, i.e, for slow fading. The fast fading is difficult to track.So, slow fading was used for path loss estimation in this simulation.

Techniques described with regard to FIG. 1 may achieve significant gainscompared to the uplink power control algorithms listed below, as shownin Table 1:

TABLE 1 SE Performance Comparison Sector spectrum Algorithm Typeefficiency Improvement (%) Full Power (No 0.6308 47% Power Control) SNRTarget Based 0.6913 (best result for 34% all SNR target) IoT Based 0.801(best result for 16% Algorithms documents)

Embodiments of the present invention may be provided, for example, as acomputer program product which may include one or more machine-readablemedia having stored thereon machine-executable instructions that, whenexecuted by one or more machines such as a computer, network ofcomputers, or other electronic devices, may result in the one or moremachines carrying out operations in accordance with embodiments of thepresent invention. A machine-readable medium may include, but is notlimited to, floppy diskettes, optical disks, CD-ROMs (Compact Disc-ReadOnly Memories), and magneto-optical disks, ROMs (Read Only Memories),RAMs (Random Access Memories), EPROMs (Erasable Programmable Read OnlyMemories), EEPROMs (Electrically Erasable Programmable Read OnlyMemories), magnetic or optical cards, flash memory, or other type ofmedia/machine-readable medium suitable for storing machine-executableinstructions.

The drawings and the forgoing description gave examples of the presentinvention. Although depicted as a number of disparate functional items,those skilled in the art will appreciate that one or more of suchelements may well be combined into single functional elements.Alternatively, certain elements may be split into multiple functionalelements. Elements from one embodiment may be added to anotherembodiment. For example, orders of processes described herein may bechanged and are not limited to the manner described herein. Moreover,the actions of any flow diagram need not be implemented in the ordershown; nor do all of the acts necessarily need to be performed. Also,those acts that are not dependent on other acts may be performed inparallel with the other acts. The scope of the present invention,however, is by no means limited by these specific examples. Numerousvariations, whether explicitly given in the specification or not, suchas differences in structure, dimension, and use of material, arepossible. The scope of the invention is at least as broad as given bythe following claims.

1. A method comprising: determining spectrum efficiency gain for a firstbase station based on a first transmitter power level; determiningspectrum efficiency loss for at least one base station other than thefirst base station based on the first transmitter power level; andselectively setting transmitter power based on the spectrum efficiencygain and spectrum efficiency loss.
 2. The method of claim 1, wherein theselectively setting transmitter power comprises setting transmitterpower to the first transmitter power level when spectrum efficiency gainis less than or equal to spectrum efficiency loss.
 3. The method ofclaim 1, further comprising: adjusting the transmitter power to a secondpower level in response to the spectrum efficiency gain exceedingspectrum efficiency loss.
 4. The method of claim 1, wherein determiningspectrum efficiency gain comprises determining:${SE}_{gain} = {{\log ( {1 + \frac{\frac{\Delta \; P}{{PL}_{0}}}{{NI}_{0} + \frac{P_{0}}{{PL}_{0}}}} )}.}$5. The method of claim 1, wherein determining spectrum efficiency losscomprises determining:${{SE}_{loss} = {\sum\limits_{i = 1}^{N}{{SE}_{loss}(i)}}},{wherein}$${{SE}_{loss}(i)} = {{\log ( {1 + \frac{\Delta \; I_{i}}{{NI}_{i}}} )} - {{\log ( {1 + \frac{\Delta \; I_{i}}{S_{i} + {NI}_{i}}} )}.}}$6. The method of claim 1, further comprising: determining path loss froma mobile station to at least one base station.
 7. The method of claim 6,wherein the determining path loss comprises neighboring base stationstransmitting path loss to the first base station.
 8. The method of claim6, wherein the determining path loss comprises the first base stationestimating path loss from the mobile station to base stations other thanthe first base station.
 9. The method of claim 1, wherein the first basestation comprises a home sector base station.
 10. The method of claim 6,wherein a mobile station performs the determining path loss for at leastone base station based in part on a preamble signal.
 11. The method ofclaim 10, further comprising: transmitting noise plus interference levelfrom the first base station to the mobile station, wherein the mobilestation determines the spectrum efficiency gain and loss based on thenoise plus interference level and the path loss.
 12. The method of claim1, wherein the mobile station performs the selectively settingtransmitter power to the first transmitter power level.
 13. The methodof claim 6, further comprising: transmitting information from a mobilestation to a first base station, wherein the first base station performsthe determining path loss for at least one base station based on theinformation.
 14. The method of claim 13, wherein the informationcomprises preamble signal strength and preamble total signal strength.15. The method of claim 13, wherein the first base station performs theselectively setting transmitter power and further comprising:transmitting the first transmitter power level to the mobile station.16. The method of claim 15, wherein the first base station performs theselectively setting transmitter power when data traffic is transmitted.17. A mobile station comprising: logic to transmit signals to a basestation at a first power level, wherein the first power level is basedin part on spectrum efficiency gain and spectrum efficiency loss,wherein spectrum efficiency gain is relative to a first base station,and wherein spectrum efficiency loss is relative to at least one basestation other than the first base station.
 18. The mobile station ofclaim 17, wherein the spectrum efficiency gain and spectrum efficiencyloss are based in part on path loss and noise plus interference levelfor at least one base station.
 19. The mobile station of claim 17,wherein the spectrum efficiency gain is based on the followingrelationship:${SE}_{gain} = {{\log ( {1 + \frac{\frac{\Delta \; P}{{PL}_{0}}}{{NI}_{0} + \frac{P_{0}}{{PL}_{0}}}} )}.}$20. The mobile station of claim 17, wherein the spectrum efficiency lossis based on the following relationship:${{SE}_{loss} = {\sum\limits_{i = 1}^{N}{{SE}_{loss}(i)}}},{wherein}$${{SE}_{loss}(i)} = {{\log ( {1 + \frac{\Delta \; I_{i}}{{NI}_{i}}} )} - {{\log ( {1 + \frac{\Delta \; I_{i}}{S_{i} + {NI}_{i}}} )}.}}$21. The mobile station of claim 17, further comprising: logic todetermine path loss based in part on a preamble signal; logic todetermine spectrum efficiency gain and loss based in part on noise plusinterference level transmitted from the first base station to the mobilestation and based in part on the path loss; and logic to determine thefirst power level based in part on a comparison between the spectrumefficiency gain and loss.
 22. The mobile station of claim 17, furthercomprising: logic to transmit information to the first base station,wherein the first base station is to determine spectrum efficiency gainand loss based in part on the information and logic to set the firstpower level at a level specified by the first base station.
 23. Themobile station of claim 22, wherein the information comprises preamblesignal strength and preamble total signal strength.
 24. A systemcomprising: at least one base station and a mobile station, wherein themobile station is to transmit signals to at least one base station at afirst power level, wherein the first power level is based on acomparison between spectrum efficiency gain and spectrum efficiencyloss, the spectrum efficiency gain is for a first base station among theat least one base station, and the spectrum efficiency loss is for atleast one base station other than the first base station.
 25. The systemof claim 24, wherein the first base station comprises: logic to transmitnoise plus interference level to the mobile station; and the mobilestation comprises: logic to determine path loss based in part on apreamble signal; logic to determine spectrum efficiency gain and lossbased in part on noise plus interference level transmitted from thefirst base station to the mobile station and based in part on the pathloss; and logic to determine the first power level based in part on acomparison between the spectrum efficiency gain and loss.
 26. The systemof claim 25, wherein the noise plus interference level comprises noiseplus interference level of the at least one base station.
 27. The systemof claim 24, wherein: the mobile station comprises: logic to transmitinformation to the first base station and logic to set the first powerlevel at a level specified by the first base station; and the first basestation comprises: logic to determine spectrum efficiency gain and lossbased in part on the information and logic to transmit the first powerlevel to the mobile station.
 28. The system of claim 27, wherein theinformation comprises preamble signal strength and preamble total signalstrength.